Original paper(Vol.46 No.1 pp.77)
Rolling contact fatigue damage in TiC- and TiN-coated steels
Miyoshi Yoshio; Ogura Keiji; Kida Katsuyuki
Abstract:The rolling contact fatigue of TiC- and TiN-coated steels was investigated. The damage was observed with a Scanning Acoustic Microscope (SAM). Measurements of X-ray residual stress and surface leaky wave velocity were also made to evaluate the damage. The SAM observation was useful to reveal the behavior of delamination and crack propagation below the surface. The results obtained are as follows.
(1) In the TiC-coated steel, cracks initiated at micro pits generated in the CVD process and propagated in a parallel direction to the rolling direction of balls at the interface between TiC film and the substrate. This resulted in the delamination and finally the peeling of TiC film.
(2) In the TiN-coated steel, micro delamination appeared at spherical defects between the film and the substrate, and grew into macro delamination. The delamination expanded and finally TiN film on the delamination peeled off the substrate.
(3) Both TiC and TiN films had an extremely large compressive residual stress. The progress of the film delamination caused an additional compressive stress in the tangential direction of the rolling direction. The residual stress measurement by X-ray was found to be effective for the evaluation of the contact fatigue damage of TiC- and TiN-coated steels.
Key Words:tribology, rolling contact fatigue damage, crack propagation, delamination, TiC coated steel, TiN coated steel, scanning acoustic microscope(SAM), X-ray residual stress